Resin-sealed semiconductor light receiving element, manufacturing method thereof and electronic device using the same

ABSTRACT

A resin-sealed semiconductor light receiving element in which a light receiving element mounted on a circuit board is sealed with a transparent resin. A mounting face of the circuit board on which the light receiving element is mounted is sealed with a transparent epoxy resin so that a light receiving surface of the light receiving element is exposed, and at least the light receiving surface of the light receiving element is sealed with a transparent silicone resin.

This application claims priority under 35 U.S.C. §119(a) on PatentApplication No. 2007-024693 filed in Japan on Feb. 2, 2007, the entirecontent of which is herein incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a resin-sealed semiconductor lightreceiving element in which a light receiving element is sealed with atransparent resin, a manufacturing method thereof, and an electronicdevice using the same.

In the field of optical sensors, sensors for optical pickups and thelike, resin-sealed devices are often used in which a semiconductorelement chip is mounted on a substrate and sealed with a transparentresin (see JP 1-209733A, Japanese Patent No. 3702998, Japanese PatentNo. 3710942, and JP 2004-79683A).

Typically, thermoset resin such as transparent epoxy resin ortransparent silicone resin is used as the transparent sealing resin.

Sealing methods often used include resin sealing the semiconductorelement chip by transfer molding using a die, or by dripping (potting)liquid resin into a mold around the placement area of the semiconductorelement chip and thermosetting the liquid resin using an oven or thelike.

In the field of optical pickups, on the other hand, the wavelength ofsemiconductor lasers is being reduced to enable high-density recordingand reproduction, and in recent years optical pickups that use bluesemiconductor lasers have been developed. And with light-receivingelements for use in the power monitors of semiconductor lasers,resin-sealed light receiving elements compatible with blue laser lighthave been commercialized.

Although transparent epoxy resin and transparent silicone resin are alsotypically used as the sealing resin for these light receiving elements,transparent epoxy resin is degraded by shortwave light such as bluelight, adversely affecting transmittance. Therefore, transparentsilicone resin having excellent light resistance to shortwave light isoften used to seal light receiving elements for use in the powermonitors of blue laser light.

FIG. 7 is a cross-sectional diagram showing a conventional resin-sealedsemiconductor light receiving element in which the light receivingelement is sealed by transparent silicone resin. In this conventionalresin-sealed semiconductor light receiving element 101, a lightreceiving element chip 103 is mounted on a circuit board 102, electrodesof the light receiving element chip 103 are connected to wiring patternsof the circuit board 102 by bonding wires 104, and the mounting face ofthe circuit board 102, the light receiving element chip 103 and thebonding wires 104 are sealed by a transparent silicone resin 105.

However, with the conventional resin-sealed semiconductor lightreceiving element 101 such as shown in FIG. 7, the following problemsarise because of using the transparent silicone resin 105 havingexcellent light resistance to short-wave light.

That is, the cure shrinkage rate of the transparent silicone resin 105is high in comparison to transparent epoxy resin, creating greaterinternal stress on the cured resin (internal deformation). Therefore,with reliability tests such as the temperature cycle test, defects suchas the bonding wires breaking inside the resin or the resin peeling fromthe interface with the circuit board readily occur, making theresin-sealed semiconductor light receiving element less reliable due tobeing less durable with respect to environmental changes such astemperature cycles in comparison to when transparent epoxy resin isused.

SUMMARY OF THE INVENTION

In view of this, the present invention, which was proposed to solve theabove problems, has as its object to provide a reliable resin-sealedsemiconductor light receiving element with excellent durability withrespect to environmental changes such as temperature cycles while usinga transparent silicone resin, a manufacturing method thereof, and anelectronic device using the same.

To solve the above problems, a resin-sealed semiconductor lightreceiving element of the present invention has a light receiving elementmounted on a circuit board and sealed with a transparent resin. Amounting face of the circuit board on which the light receiving elementis mounted is sealed with a transparent epoxy resin so that a lightreceiving surface of the light receiving element is exposed, and atleast the light receiving surface of the light receiving element issealed with a transparent silicone resin.

With this resin-sealed semiconductor light receiving element of thepresent invention, the mounting face of the circuit board on which thelight receiving element is mounted is sealed with a transparent epoxyresin so that the light receiving surface of the light receiving elementis exposed, and at least the light receiving surface of the lightreceiving element is sealed with a transparent silicone resin.Consequently, the mounting face of the circuit board and the connectionpoints of the bonding wires on the circuit board are sealed bytransparent epoxy resin, and given that the cure shrinkage rate of thistransparent epoxy resin is low, there is little internal stress(internal deformation) on the cured resin. Therefore, defects such asthe bonding wires breaking inside the resin or the resin peeling fromthe interface with the circuit board do not occur, and durability withrespect to environmental changes such as temperature cycles isexcellent, enabling high reliability to be obtained.

Also, at least the light receiving surface of the light receivingelement is sealed with transparent silicone resin, and given that thistransparent silicone resin has excellent light resistance to shortwavelight, the light receiving characteristics of the light receivingelement are not impaired.

A manufacturing method of a resin-sealed semiconductor light receivingelement of the present invention includes the steps of mounting aplurality of light receiving elements on a circuit board, electricallyconnecting each of the light receiving elements to the circuit board,sealing a mounting face of the circuit board on which the lightreceiving elements are mounted with a transparent epoxy resin so that alight receiving surface of each of the light receiving elements isexposed, sealing the light receiving surfaces of the light receivingelements and a top surface of the transparent epoxy resin with atransparent silicone resin, and cutting the circuit board, thetransparent epoxy resin and the transparent silicone resin by dicing toseparate the light receiving elements on the circuit board.

The manufacturing method of a resin-sealed semiconductor light receivingelement of the present invention enables a plurality of the resin-sealedsemiconductor light receiving elements of the present invention to bemanufactured at the same time.

Further, an electronic device of the present invention uses theresin-sealed semiconductor light receiving element of the presentinvention.

Since the electronic device of the present invention uses theresin-sealed semiconductor light receiving element of the presentinvention, similar effects to this resin-sealed semiconductor lightreceiving element can be achieved, and the durability of the electronicdevice itself is also improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing an embodiment of a resin-sealedsemiconductor light receiving element of the present invention.

FIG. 2 is a graph showing test results obtained by performing atemperature cycle test on the resin-sealed semiconductor light receivingelement of the embodiment of FIG. 1 and a conventional semiconductorlight receiving element.

FIG. 3 shows an embodiment of the manufacturing method of the presentinvention.

FIG. 4 shows an embodiment of the manufacturing method of the presentinvention.

FIG. 5 shows an embodiment of the manufacturing method of the presentinvention.

FIG. 6 shows an embodiment of the manufacturing method of the presentinvention.

FIG. 7 is a cross-sectional view showing a conventional resin-sealedsemiconductor light receiving element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the drawings.

FIG. 1 is a cross-sectional view showing an embodiment of a resin-sealedsemiconductor light receiving element of the present invention. Theresin-sealed semiconductor light receiving element 1 of the presentembodiment is used in a power monitor of a blue semiconductor laser inthe field of optical pickups.

With the resin-sealed semiconductor light receiving element 1, a lightreceiving element chip 12 is fixed to a chip mounting portion 11 dprovided on a mounting face 11 a of a circuit board 11 via a conductivepaste or the like. Electrodes (not shown) of the light receiving elementchip 12 are connected to wiring pattern terminals 11 p provided on themounting face 11 a of the circuit board 11 by bonding wires 13 composedof Au.

The mounting face 11 a of the circuit board 11 is sealed with atransparent epoxy resin layer 14 so that a light receiving surface 12 aof the light receiving element chip 12 is exposed, and the lightreceiving surface 12 a of the light receiving element chip 12 and a topsurface 14 a of the transparent epoxy resin layer 14 is sealed with atransparent silicone resin layer 15.

The transparent epoxy resin layer 14 and the transparent silicone resinlayer 15 are formed by dripping (potting) a liquid transparent epoxyresin or transparent silicone resin into a mold provided so as toenclose the placement area of the light receiving element chip 12 andthermosetting the liquid resin using an oven or the like. The mold canbe formed by insert molding on the circuit board 11 using a die or byadhesion on the circuit board 11 using an adhesive or the like.

This results in the mounting face 11 a of the circuit board 11 and theconnection points (second bonding points) of the bonding wires 13 on thecircuit board 11 being sealed by the transparent epoxy resin layer 14,and the light receiving surface 12 a of the light receiving element chip12 being sealed by the transparent silicone resin layer 15.

Here, given that the cure shrinkage rate of transparent silicone resinis high in comparison to transparent epoxy resin, there is significantinternal stress (internal deformation) on the cured transparent siliconeresin. Therefore, when reliability tests such as the temperature cycletest, for example, are performed, defects such as the resin peeling fromthe interface with the circuit board or the bonding wires breakinginside the resin (primarily breakage at second bonding points) readilyoccur.

In contrast, there is little internal stress (internal deformation) onthe cured transparent epoxy resin given that the cure shrinkage rate oftransparent epoxy resin is small. Therefore, when the mounting face 11 aof the circuit board 11 and the connection points of the bonding wires13 on the circuit board 11 are sealed by the transparent epoxy resinlayer 14 and the transparent epoxy resin layer 14 is cured, neitherpeeling of the transparent epoxy resin layer 14 from the interface withthe mounting face 11 a of the circuit board 11 nor breakage of thebonding wires 13 inside the transparent epoxy resin layer 14 readilyoccur. Sufficiently high reliability can be achieved without suchpeeling or breakage occurring when reliability tests such as thetemperature cycle test are performed.

In the present embodiment, the thickness of the transparent epoxy resinlayer 14 is controlled so that the mounting face 11 a of the circuitboard 11 and the connection points of the bonding wires 13 are securelysealed by the transparent epoxy resin layer 14, thereby enabling highreliability to be reproduced.

At the same time, the thickness of the transparent epoxy resin layer 14is controlled so as to be less than the thickness of the light receivingelement chip 12, so as to ensure that the light receiving surface 12 aof the light receiving element chip 12 is not covered by the transparentepoxy resin layer 14. This enables the light receiving surface 12 a ofthe light receiving element chip 12 to be covered and sealed by only thetransparent silicone resin layer 15, resulting in light that has onlypassed through this transparent silicone resin layer 15 being incidenton the light receiving surface 12 a of the light receiving element chip12.

Given that the resin-sealed semiconductor light receiving element 1 ofthe present embodiment is used in the power monitor of a bluesemiconductor laser as aforementioned, a drop in the light receivingcharacteristics is forestalled by employing a configuration in whichlight that has only passed through this transparent silicone resin layer15 having excellent light resistance to shortwave light is incident onthe light receiving surface 12 a of the light receiving element chip 12.If light were incident via the transparent epoxy resin layer 14, thetransparent epoxy resin layer 14 would be degraded by the shortwavelight, adversely affecting transmittance and reducing in the lightreceiving characteristics.

The graph in FIG. 2 shows test results obtained by performing thetemperature cycle test on the resin-sealed semiconductor light receivingelement 1 of the present embodiment and a conventional semiconductorlight receiving element sealed using only transparent silicone resin.This test investigated the failure rate (bonding wire breakage rate) ofthe resin-sealed semiconductor light receiving element 1 and theconventional semiconductor light receiving element in an environment inwhich temperature cycles of −40° C. to +100° C. were repeated.

As evident from the FIG. 2 graph, extremely high reliability wasobtained with the resin-sealed semiconductor light receiving element 1of the present embodiment, with no failures occurring after 2000 cycles.In contrast, the conventional semiconductor light receiving element wasmarkedly inferior in terms of reliability, with failures occurring ataround 100 cycles and a 40% failure rate after 500 cycles.

Next, an embodiment of the manufacturing method of the present inventionwill be described with reference to FIGS. 3 to 6. With the manufacturingmethod of the present embodiment, a plurality of the resin-sealedsemiconductor light receiving elements 1 shown in FIG. 1 aremanufactured at the same time.

Firstly, as shown in FIG. 3, a plurality of light receiving elementchips 12 are arranged on and fixed to a mounting face 11 a of a circuitboard 11A by applying a conductive paste or the like to the mountingface 11 a, and electrodes (not shown) of each light receiving elementchip 12 are connected to wiring pattern terminals 11 p of the circuitboard 11A by bonding wires 13 composed of Au or the like.

Next, as shown in FIG. 4, the mounting face 11 a of the circuit board11A and the connection points (second bonding points) of the bondingwires 13 on the circuit board 11A are coated with a transparent epoxyresin layer 14 by dripping (potting) a liquid transparent epoxy resinonto the mounting face 11 a of the circuit board 11A. The transparentepoxy resin layer 14 is then thermoset using an oven or the like to sealthe mounting face 11 a of the circuit board 11A and the connectionpoints of the bonding wires 13 on the circuit board 11A with thetransparent epoxy resin layer 14.

At this time, the transparent epoxy resin layer 14 is formed so as to bethinner than the light receiving element chips 12, exposing the lightreceiving surfaces 12 a of the light receiving element chips 12.

Next, as shown in FIG. 5, the top surface 14 a of the transparent epoxyresin layer 14 and the light receiving surfaces 12 a of light receivingelement chips 12 are coated with a transparent silicone resin layer 15by dripping (potting) a liquid transparent silicone resin. Thetransparent silicone resin layer 15 is then thermoset using an oven orthe like to seal the transparent epoxy resin layer 14 and the lightreceiving surfaces 12 a of light receiving element chips 12 with thetransparent silicone resin layer 15.

Next, as shown in FIG. 6, the circuit board 11A, the transparent epoxyresin layer 14 and the transparent silicone resin layer 15 are dividedby cutting along prescribed lines by dicing using a blade 21 to separatethe light receiving element chips 12 and obtain a plurality ofresin-sealed semiconductor light receiving elements 1 composed of thecircuit board 11, the light receiving element chip 12, the bonding wires13, the transparent epoxy resin layer 14, the transparent silicone resinlayer 15 and the like as shown in FIG. 1.

Here, the dicing sheet is stuck to the underside of the circuit board11A and dicing is performed from the sealing resin side, but the dicingsheet may conversely be stuck to the top surface of the sealing resinand dicing performed from the circuit board 11A side.

The present invention encompasses not only a resin-sealed semiconductorlight receiving element but an electronic device that applies thisresin-sealed semiconductor light receiving element. The electronicdevice is an optical pickup or the like.

The present invention may be embodied in other forms without departingfrom the gist or essential characteristics thereof. The foregoingembodiments are therefore to be considered in all respects asillustrative and not limiting. The scope of the invention is indicatedby the appended claims rather than by the foregoing description, and allmodifications and changes that come within the meaning and range ofequivalency of the claims are intended to be embraced therein.

1. A resin-sealed semiconductor light receiving element in which a lightreceiving element mounted on a circuit board is sealed with atransparent resin, wherein a mounting face of the circuit board on whichthe light receiving element is mounted is sealed with a transparentepoxy resin so that a light receiving surface of the light receivingelement is exposed, and at least the light receiving surface of thelight receiving element is sealed with a transparent silicone resin. 2.A manufacturing method of a resin-sealed semiconductor light receivingelement, comprising the steps of: mounting a plurality of lightreceiving elements on a circuit board; electrically connecting each ofthe light receiving elements to the circuit board; sealing a mountingface of the circuit board on which the light receiving elements aremounted with a transparent epoxy resin so that a light receiving surfaceof each of the light receiving elements is exposed; sealing the lightreceiving surfaces of the light receiving elements and a top surface ofthe transparent epoxy resin with a transparent silicone resin; andcutting the circuit board, the transparent epoxy resin and thetransparent silicone resin by dicing to separate the light receivingelements on the circuit board.
 3. An electronic device using aresin-sealed semiconductor light receiving element as claimed in claim1.